1. Field
The present disclosure relates to a method for controlling a fuel cell system.
2. Description of the Related Art
A solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA), in which an anode electrode is disposed on one surface of an electrolyte membrane, which is a proton-conductive polymer ion-exchange membrane, and a cathode electrode is disposed on the other surface of the electrolyte membrane. The membrane electrode assembly and separators, sandwiching the membrane electrode assembly, constitute a power generation cell (unit cell). Typically, a predetermined number of power generation cells are stacked and, for example, mounted in a fuel cell vehicle (a fuel cell electric automobile or the like) as a vehicle fuel cell stack.
When the fuel cell is operated, a fuel gas (such as hydrogen gas) is supplied to the anode electrode and an oxidant gas is supplied to the cathode electrode. Therefore, the fuel cell has a fuel gas tank, a fuel gas pump, a fuel gas supply channel, an oxidant gas pump, a fuel gas discharge (circulation) channel, a humidifier, an oxidant gas supply channel, an oxidant gas discharge channel, and the like. These components constitute a fuel cell system.
Typically, compressed air is used as the oxidant gas, because air is abundant and compressed air can be easily obtained by compressing air. In this case, an oxidant gas pump (air pump) compresses air and supplies the compressed air to the cathode electrode. The supply pressure of compressed air, that is, the internal pressure of the cathode electrode is controlled by adjusting the opening degree of a pressure adjusting valve that is disposed in the oxidant gas discharge channel, as described in Japanese Unexamined Patent Application Publication No. 2006-196231 (in particular, paragraph [0016]).
The air pump compresses and supplies air as a motor rotates. As the rotation speed of the motor increases, the compressed air can be supplied at a higher flow rate. In other words, when the motor is rotating at the lowest rotation speed, the air flow rate is the lowest. The air flow rate at this time is the lowest supply flow rate.